This invention relates to a valve operating mechanism for a four-cycle engine and more particularly to an improved valve operating mechanism for such engines.
As is well-known, the performance of an engine is directly related to its ability to breathe. That is, the ability to induct a large charge in a short time period and also exhaust a large charge in a short time period is important to the development of good power for the engine. This requires rapid opening of the intake and exhaust valves. Normally, the valves are operated either directly by the cam lobes, or, in many instances, the valves are operated by a rocker arm which is in turn operated by the cam. There are some advantages in being able to employ rocker arm so as to amplify the motion of the valves from that permitted by the cam configuration. However, in order to provide rapid opening of the valves through a rocker arm actuator, it is necessary to form a concave configuration on the cam lobe in the ramp leading to the fully-opened position. However, such concave cam configurations are difficult to form and require special grinding tool.
In a like manner, there is a desirability to close the intake and exhaust valves at a less rapid rate than they are opened. The reason for this is that rapid closure of the intake and exhaust valves can cause bouncing of the valve. That is, if the valve is closed too rapidly, the impact with the valve seat may cause the valve to bounce open. Although this can be avoided through the use of heavy springs, these heavy springs increase the load on operation of the valve train and can cause reduced power.
In order to provide restricted rate of closure of the valves along with rapid opening, it has also been necessary to form concave cam profiles which have the defects as aforenoted.
It is, therefore, a principal object of this invention to provide an improved valve operating mechanism for an internal combustion engine.
It is a further object of this invention to provide an improved cam and rocker arm valve actuating system wherein rapid rates of valve opening and slower rates of valve closing can be accomplished without using especially formed cam lobes.
It is a further object of this invention to provide an improved follower surface configuration for a valve actuating rocker arm that permits rapid opening and slow closing with relatively conventional and easily formed cam lobe configurations.